Connection control apparatus

ABSTRACT

There is provided a connection control apparatus which, even when a plurality of such connection control apparatuses are connected to a bus such as the 1394 bus through which packet-based bidirectional serial communication is possible and to which a plurality of AV devices can be connected, makes it possible to know to which connection control apparatus the right of controlling each device connected to the bus belongs by collecting information about the control status of each connection control apparatus, thereby to carry out a high level of management of connections to and controls of the bus. Each connection control apparatus connected to a bus, through which packet-based bidirectional serial communication is possible and to which a plurality of AV devices can be connected, comprises a control flag register and a control information register for storing the status of connection of the present device through the bus to other devices as well as the status of connection of the other devices to one another through the bus.

BACKGROUND OF THE INVENTION

This invention relates generally to a connection control apparatus foruse in a communication network and more particularly to a connectioncontrol apparatus for controlling, in a network with a bus such as ahigh-speed serial bus IEEE 1394 (refer to “IEEE Standard for a HighPerformance Serial Bus”, IEEE Standard 1394-1995) to which a personalcomputer, its peripheral device and/or an audio visual device(hereinafter referred to as a “AV device”) can be connected, thosedevices connected to such a bus.

In recent years, personal computers become common in homes, and varioustechniques have been and are being developed for improving the usabilityof such personal computers by their users. It has also become common foraudio and visual information to be treated in digital form. For example,data from a digital video camera can be processed in a personal computerat home. Under such circumstances, new bus systems such as a USB(Universal Serial Bus) and an IEEE 1394 bus have been proposed as newtechnology for improving the connectability between a computer and itsperipheral device, such as a printer or an image scanner, and actuallybeen brought to market in some fields.

As compared to the USB that needs interfacing by a computer for theconnection between its peripheral devices, the IEEE 1394 bus does notneed any interfacing by a computer for such connection. The latter cantherefore be used not only for connecting a personal computer to itsperipheral devices such as a printer, a hard disc drive, or an imagescanner, but also for transferring main and control signals among videodevices such as a digital video camera and audio devices. Since it isthus possible to construct a network by connecting a plurality ofdevices complying with the IEEE 1394 standard (hereinafter referred tosimply as “1394 devices”), this standard is considered to be a promisingstandard for use in a LAN for home networking.

FIG. 9 shows, by way of example, a network constructed to connect AVdevices, which are 1394 devices, using an IEEE 1394 bus. In the exampleshown in FIG. 9, five AV devices 80 a to 80 e all of which are 1394devices are connected to an IEEE 1394 bus B10. In order to associate anisochronous channel when transferring data between AV devices, each AVdevice is provided with a master plug register (MPR) and a plug controlregister (PCR) as prescribed in the IEC 61883 standard (“ConsumerAudio/Video Equipment—Digital Interface—Part 1: General”, ReferenceNumber CEI/IEC 61883-1: 1998).

Each of these registers comprises an input and an output register foraudio data and video data, and each master plug register is providedwith an input master plug register (iMPR) and an output master plugregister (oMPR), while each plug control register is provided with aninput plug control register (iPCR) and an output plug control register(oPCR).

In the example shown in FIG. 9, the AV devices 80 a to 80 d compriseiMPRs 82 a to 82 d, respectively, and the AV device 80 e comprises anoMPR 84. The iMPR 82 a to 82 d comprise iPCRs 86 and 88, an iPCR 90, aniCPR 92 and iCPRs 94 and 96, respectively, and the oMPR 84 comprises anoPCR 98. In FIG. 9, shown at C10 is an isochronous channel that isestablished to transmit or receive data when an isochronous transfer ofthe data should take place between AV devices connected to the IEEE 1394bus B10.

FIG. 10 illustrates detailed formats for the above-described registers,wherein (a) shows the format for the output master plug register (oMPR),(b) the format for the input master plug register (iMPR), (c) the formatfor the output plug control register (oPCR) and (d) the format for theinput plug control register (iPCR). These formats have beenstandardized. The numerals shown at the bottom of each format representthe numbers of bits of respective data constituting the relevant format.

Each of the AV devices 80 a to 80 e comprises a respective single one ofthe iMPRs 82 a to 82 d and oMPR 84, each of which manages the number ofplug control registers in a respective one of the AV devices, i.e.,iPCRs 86 to 96 and oPCR 98. The number of oPCRs and iPCRs which can bepresent in one AV device is thirty-one at maximum. The oPCR and IPCRinclude, for the information required to establish a connection, fieldsFC2 and FD2 each for storing information indicating the presence of abroadcast connection, fields FC3 and FD3 each for storing informationindicating the number of point-to-point connections, fields FC5 and FD5each for storing information indicating an isochronous channel numberand so on, respectively. The oPCR further includes a field FC6 forstoring information indicating a transfer rate of isochronous data flowand a field FC8 for storing information indicating a bandwidth.Addresses of the registers in which the MPR and PCR are described aredescribed, as shown in FIG. 11, in addresses from FF FF F0 09 00h to FFFF F0 09 FFh (h represents hexadecimal notation) within a CSR (Commandand Status Register) space defined in the IEEE 1394 standard. FIG. 11illustrates a structure of the CSR space according to the IEEE 1394standard.

For isochronous data output from an AV device, a path for sending theisochronous data between AV devices can be determined by making a propersetting to these PCRs, whereby it is possible to have a data transfermade between any arbitrary AV devices.

Referring again to FIG. 9, the concept of connection utilizing PCRs willbe described. The connection utilizing PCRs is categorized into twotypes, i.e., a point-to-point connection and a broadcast connection.

The point-to-point connection is a connection in which an oPCR of an AVdevice is connected through an isochronous channel to an iPCR of anotherAV device. This type of connection corresponds, for example, to the dataflow between the oPCR 98 of the AV device 80 e and the iPCR 90 of the AVdevice 80 b shown in FIG. 9. This connection is protected so that therelevant registers can be rewritten only by the device that establishedthis connection, or by the relevant control application program.

It is also possible to have a plurality of point-to-point connectionspresent with respect to the same single PCR. In the example shown inFIG. 9, this corresponds to the connection between the oPCR 98 of the AVdevice 80 e and the iPCR 94 of the AV device 80 d. In this example,there are three point-to-point connections which use the sameisochronous data flow.

The broadcast connection is composed of a broadcast-out connection forassociating one oPCR of an AV device only with one isochronous channeland a broadcast-in connection for associating one iPCR of another AVdevice only with one isochronous channel.

In the example of FIG. 9, the association of the oPCR 98 of the AVdevice 80 e with a broadcast channel number (usually set to “63”) forthe isochronous data is a broadcast-out connection, while theassociation of the iPCR 92 of the AV device 80 c with the broadcastchannel number for the isochronous data is a broadcast-in connection.

These two types of broadcast connections are established independentlyof the mutual relation in the condition of the sender and the recipient.Any device other than those devices or control application programswhich have established the broadcast connection can alter (or rewrite)the PCR not only to cut the connection but also to allocate thebroadcast isochronous channel of the currently transferring device.

The data transmission/reception after the establishment of a connectionbetween AV devices can be started by controlling the sending andreceiving AV devices by AV/C (Audio Video Control) commands defined in“AV/C Digital Interface Command Set Version 3.0”, 1394 TradeAssociation, Apr. 15, 1998 or “AV/C Tape Recorder/Player SubunitSpecification Version 2.1”, 1394 Trade Association, Jan. 11, 1998. AsAV/C commands, a play command, a stop command, a fast forward command, arewind command, a record command, a slow forward command and so on areavailable. The transmission/reception of the AV/C commands onto/from the1394 bus is carried out in accordance with the Function Control Protocolprescribed in the EC 61883 Standard. When an isochronous transfer iscompleted, the connection is released by clearing the setting to thetransmitting/receiving AV devices.

Based on the above-described setting to the PCRs, a controller(connection control apparatus) can establish or release a connectionbetween 1394-compliant AV devices. One example of such establishment andrelease of a connection between AV devices will now be described.

FIG. 12 illustrates the conventional way of controlling connections. Itis here assumed that four 1394 devices 100 a to 100 d and one controller102 are connected to a 1394 bus B12 as shown in FIG. 12. For the sake ofsimplicity, it is further assumed that the 1394 devices 100 a to 100 dhave no function of controlling connections.

The controller 102 can switch two connection pairs between the 1394device 100 a and the 1394 device 100 c and between the 1394 device 100 band the 1394 device 100 d to two connection pairs between the 1394device 100 a and the 1394 device 100 d and between the 1394 device 100 band the 1394 device 100 c and vice versa.

In this case, since there is only one controller 102 on the 1394 bus B12and each 1394 device has only one connection established, controls ofthe 1394 devices 100 a to 100 d such as playing and recording by theirAV/C commands will not conflict with each other.

We now consider another case where six 1394 devices 104 a to 104 f andthree controllers 106 a to 106 c are connected to a 1394 bus B14 asshown in FIG. 13. FIG. 13 is an illustration showing one conventionalbus structure and exemplary connections made therein from which problemsof the prior art will be apparent. For the sake of simplicity, it isassumed that the 1394 devices 104 a to 104 f have no connection controlfunctions.

Let's consider a situation where the 1394 devices 104 a and 104 b areconnected respectively to the 1394 devices 104 d and 104 c by thecontroller 106 a (as indicated by solid-line arrows in FIG. 13), the1394 device 104 a is connected to the 1394 device 104 e by thecontroller 106 b (as indicated by a dotted arrow in FIG. 13) and the1394 device 104 a is connected to the 1394 device 104 f by thecontroller 106 c (as indicated by a dot-and-dash arrow in FIG. 13).

In this situation, three connections overlap with each other at the 1394device 104 a. In the situation shown in FIG. 13, plural controllers 106a to 106 c coexist on the same 1394 bus B14. When the connection set bythe controller 106 a between the 1394 device 104 a and the 1394 device104 d is a point-to-point connection, this connection will be protectedas described before. However, even if the connection between thesedevices is protected, the control of the 1394 devices can also be doneby other controllers 106 b and 106 c. This is because, in the case of apoint-to-point connection, the connection between the 1394 devices isprotected but the control to these 1394 devices is not protected.

Let's consider a case where a dubbing operation is performed between the1394 device 104 a and the 1394 device 104 d. In this case, it is assumedthat the 1394 devices 104 a and 104 d are video devices.

Suppose that the controller 106 a controls a connection between the 1394devices 104 a and 104 d and protects the connection. By means of thisprotection, the connection between the 1394 devices 104 a and 104 d isreliably protected. However, since no protection is made with respect tothe control of 1394 devices as described above, there may occur such aproblem that the dubbing operation is disturbed when an AV/C commandsuch as a play command, a record command and a stop command is issued tothe 1394 device 104 a, 104 d, for example, by the controller 106 b.

The above problem seems to be solved by applying, to the way ofcontrolling 1394 devices, such an idea of protection that when aconnection between 1394 devices is controlled by a certain controllerthe right of controlling a transmitting operation, a receiving operationand so on is given to that controller. However, in the case such as thatshown in FIG. 13 where up to three connections have been established forthe 1394 device 104 a, it is not known to which controller the right ofcontrolling the 1394 device 104 a belongs. Thus, there is a problem thatit cannot eventually be determined to which controller the right ofcontrolling the 1394 device 104 a belongs.

When only two controllers are connected to a 1394 bus, it will easily bedetermined that any connections other than those made by the presentcontroller have been made by another controller. However, when there aremore than two controllers connected and when only one connection hasbeen established in each 1394 device as in the 1394 devices 104 b, 104c, 104 d, 104 e and 104 f, there will occur the problem that it is notpossible for a given controller to know by which controllersconnections, other than those established by this given controller, havebeen established.

SUMMARY OF THE INVENTION

It is therefore an object of the present invention to provide aconnection control apparatus which makes it possible, even when aplurality of such connection control apparatuses have been connected toa bus such as a 1394 bus through which bidirectional serialcommunication is possible by means of packets and to which a pluralityof AV devices can be connected, to know to which connection controlapparatus the right of controlling each device connected to the busbelongs by collecting information about the control statuses of therespective connection control apparatuses, thereby to carry out advancedmanagement of connections onto and controls of the bus.

In order to solve the above problems, according to a first aspect of thepresent invention, there is provided a connection control apparatusadapted to be connected to a bus through which packet-basedbidirectional serial communication can be performed and to which aplurality of apparatuses can be connected, the connection controlapparatus comprising memory means for storing a status of logicalconnection of the present apparatus through the bus to other apparatusesand for storing a status of logical connection among the otherapparatuses through the bus.

The above invention may further be characterized by comprising readingmeans for reading the statuses of connection stored in the memory meansof the other apparatuses through the bus.

The above invention may further be characterized in that the status ofconnection includes an identifier of a destination apparatus.

The above invention may further be characterized in that the status ofconnection includes information indicative of priorities of connections.The above invention may further be characterized in that the bus is abus which complies with the IEEE 1394 bus standard.

The above invention may further be characterized in that the status ofconnection includes history information of updating the status ofconnection, the connection control apparatus further comprising updatingmeans for comparing the status of a connection read by the reading meanswith that stored in the present apparatus to update the status of theconnection stored in the present apparatus when the status of theconnection stored in the present apparatus is older.

The above invention may further be characterized in that the status ofthe connection includes information about another apparatus which hasreleased a connection established by the present apparatus.

The above invention may further be characterized by further comprisingdetermination means for determining a right of controlling eachapparatus connected to the bus based on the information indicative ofpriorities.

In order to solve the above-described problems, according to a secondaspect of the present invention, there is provided a connection controlapparatus connected to an IEEE 1394 bus for controlling a connectionbetween apparatuses each having a plug control register, the connectioncontrol apparatus comprising a plug control register controlling sectionfor transmitting/receiving packets through the 1394 bus to control theplug control registers of other apparatuses and to generate connectioninformation between the apparatuses, a control information register forstoring the connection information generated by the plug controlregister controlling section, a control flag register for indicating apresence of an update of the control information register and an amountof information in the control information register, an apparatus controlsection for transmitting/receiving packets through the 1394 bus tocontrol operations of those apparatuses connected to the 1394 bus, andan apparatus control right judging section for collecting values in thecontrol information register and the control flag register with respectto all the apparatuses connected to the same bus to determine thoseapparatuses whose controls are to be allowed and to inform the apparatuscontrol section of those apparatuses.

The above invention may further be characterized in that the controlflag register comprises a data-length field for representing an amountof information in the control information register, and a historyinformation field whose value represents a presence of an update of thecontrol information register and is incremented each time the controlinformation register is updated.

The above invention may further be characterized in that the controlinformation register comprises a first field for representing whetherthe plug control register is for input or for output, a second field forrepresenting a serial number of the plug control register provided inthe apparatus, a third field for representing a value in apoint-to-point connection counter of the plug control register, a fourthfield for representing a type of the control information register, andobjective bus ID and objective physical ID fields for representing a busID and a physical ID of the apparatus provided with the plug controlregister.

The above invention may further be characterized in that the fourthfield for representing the type of the control information register is afield for storing a value indicating that information about the plugcontrol register set by the present apparatus is stored or a valueindicating that information about the plug control register by which thepresent apparatus released a point-to-point connection established byanother apparatus is stored.

The above invention may further be characterized in that the controlflag register and the control information register are arranged in acontrol status register space as defined in the IEEE 1212 standard.

Thus, according to the present invention, even when a plurality ofconnections are set to one apparatus by a plurality of connectioncontrol apparatuses, it is possible to give the right of controlling anapparatus to one specific connection control apparatus, so that theapparatus can be controlled without any conflict from other connectioncontrol apparatuses.

It is also possible to know by which connection control apparatus aconnection between apparatuses has been established even when there aremore than two connection control apparatuses present on the bus, so thata high level of management of connections of apparatuses present on thebus can be achieved.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of a connection control apparatus provided inaccordance with one embodiment of the invention;

FIG. 2 is an illustration showing addresses of CFR 44 and CIR 46;

FIG. 3 is an illustration showing formats of the CFR 44 and CIR 46,wherein (a) is the format of the CFR and (b) is the format of the CIR;

FIG. 4 is an illustration showing generally the process performed in theconnection control apparatus according to the embodiment of theinvention;

FIG. 5 is a detailed flowchart of the process (step S14) for updatingthe CFR 44 and CIR 46 of FIG. 4;

FIG. 6 is an illustration showing an exemplary AV-device control rightinformation table created in the process of step S22;

FIG. 7 is a detailed flowchart of the process (step S22) for creatingthe AV-device control right information table of FIG. 4;

FIG. 8 is a detailed flowchart of the process (step S24) for judging theAV-device control right of FIG. 4;

FIG. 9 is an illustration showing a network constructed for AV devices(which are 1394 devices) with an IEEE 1394 bus;

FIG. 10 is an illustration showing detailed formats of the registers,wherein (a) is the format of the output master plug register (oMPR),(b.) the format of the input master plug register (iMPR), (c) the formatof the output plug control register (oPCR), and (d) the format of theinput plug control register (iPCR);

FIG. 11 is an illustration showing the structure of the IEEE 1394 CSRspace;

FIG. 12 is an illustration showing the conventional connection control;and

FIG. 13 is an illustration showing the conventional bus structure andexemplary connections made therein from which the problem of the priorart is seen.

DESCRIPTION OF THE PREFERRED EMBODIMENT OF THE INVENTION

A connection control apparatus according to an embodiment of the presentinvention will now be described in detail with reference to theaccompanying drawings.

FIG. 1 is a block diagram of a connection control apparatus provided inaccordance with an embodiment of the invention when applied to a 1394bus system.

In FIG. 1, the connection control apparatus 10 according to theinvention generally comprises a connection control section 20, a 1394transaction layer 30, a 1394 link layer 32, a 1393 physical layer 34,and a serial bus management section 40.

The connection control section 20 comprises a PCR control section 22, anAV-device control section 24, and an AV-device control right judgingsection 26. The serial bus management section 40 is provided with a 1394CSR space 42 described above with reference to FIG. 11, which spaceincludes a control flag register (hereinafter referred to as “CFR”) 44and a control information register (hereinafter referred to as “CIR”)46. These registers are provided, in brief, for storing the statuses ofrespective devices connected to the 1394 bus, for example, the status ofconnection between AV devices and the like.

FIG. 2 shows addresses of the CFR 44 and CIR 46. The CFR 44 occupiesonly one quadlet (four bytes) in the 1394 CSR space, while the CIR 46 isprovided by reserving in the 1394 CSR space an area having a certainwidth. The CFR 44 and the CIR 46 are provided in an empty area (forexample, in those addresses after FF FF F0 30 00h) of the 1394 CSR spaceshown in FIG. 11. In FIG. 2, 128 quadlets following the CFR address areassigned to the CIR 46.

FIG. 3 is an illustration showing formats of the CFR 44 and CIR 46,wherein (a) is the format of the CFR and (b) is the format of the CIR.

First, each field of the CFR format will be described. A field F1 is afield for storing a flag indicating that this is a connection controlapparatus. In the example of FIG. 3, “c” is indicated in this field F1.A field F2 is a field for storing a quadlet length of the CIR 46following the CFR 44. In the example of FIG. 3, “data length” isindicated in this field F2. A field F3 is a field for storinginformation about the CIR 46 updated by additions and/or deletions. Inthe example of FIG. 3, “history information” is indicated in this fieldF3. A field F4 is a reserved field, and “reserved” is indicated in thisfield F4 shown in FIG. 3. The history information contained in the fieldF3 is increased by one (incremented) each time the CIR 46 is updated.

Next, each field of the CIR format will be described. A field F5 is afield for storing information indicative of whether the relevant PCR isfor input or output, in which “1” is stored in the case of an oPCR and“0” is stored in the case of an iPCR. In FIG. 3, “p” is indicated inthis field F5. A field F6 is a field for storing the number of the PCRmounted in the AV device. In the example of FIG. 3, “PCR[i]” isindicated in this field F6. A field F7 is a reserved area, and “rsv” isindicated in this field F7 in FIG. 3. A field F8 is a field for storinga counter value of point-to-point connections of the relevant PCR. Inthe example of FIG. 3, “p-p count” is indicated in this field F8. Thisfield F8 contains information indicating the order number of theconnection when a plurality of connections have been made.

A field F9 is a field for storing the type of the relevant CIR 46. Whencontaining a value “00”, this field indicates that the relevant CIRcontains information about the PCR set by the present connection controlapparatus. When containing a value “01”, this field indicates that therelevant CIR contains information about the PCR set by the connectioncontrol apparatus when a point-to-point connection established byanother connection control apparatus has been released. The value storedin the field F8 and the information stored in the field F9 indicate thepriority of the connection.

Values “10” and “11” are treated as reserved codes and not used atpresent. In the example of FIG. 3, “Info” is indicated in this field F9.Fields F10 and F11 are fields for storing a higher order ten-bit bus IDand a lower order six-bit physical ID, respectively, of the node ID ofan AV device for which the PCR control section 22 has set the PCR. Inthe example of FIG. 3, “objective bus ID” and “objective physical ID”are indicated in these fields F10 and F11, respectively. Any devicesconnected to a 1394 bus are called “nodes” and require IDs in order tobe discriminated from each other. In other words, it will be possible tospecify the destination device by storing its “p”, “PCR[i]”, “objectivebus ID”, and “objective physical ID”.

As shown in FIG. 3 (b), an amount of data equal to one quadlet is neededto store information about a connection between devices coupled to the1394 bus. Since the CIR 46 comprises 128 quadlets, it can storeinformation about up to 128 connections.

Referring back to FIG. 1, the PCR control section 22 transmits packetsthrough the 1394 transaction layer 30, the 1394 link layer 32 and the1394 physical layer 34 in order to rewrite an arbitrary PCR of anarbitrary AV device on the 1394 bus. Simultaneously with the rewritingof the PCR, the PCR control section 22 updates the CFR 44 and, at thesame time, performs addition and/or deletion with respect to the CIR 64.The rules for rewriting the CFR 44 and CIR 64 will be described later indetail.

The AV-device control section 24 sends AV commands through the 1394transaction layer 30, the 1394 link layer 32, and the 1394 physicallayer 34 to that of the AV devices connected to the 1394 bus which hasbeen allowed by the AV-device control right judging section 26, tothereby control operations of that device such as play, stop, rewind andrecord.

The AV-device control right judging section 26 reads the informationstored in the CFR 44 and the CIR 46 arranged in the CSR space 42 of thepresent connection control apparatus and also reads the informationstored in the CFRs and CIRs arranged in the CSR spaces of otherconnection control apparatuses present on the 1394 bus. The AV-devicecontrol right judging section 26 then determines for each AV device theconnection control apparatus which has the right of controlling that AVdevice based on the read information, and informs the AV-device controlsection 24 of those AV devices which the present connection controlapparatus can control.

An outline of operation of the connection control apparatus provided inaccordance with the embodiment of the invention having the abovestructure will now be described.

FIG. 4 shows a general process in the connection control apparatusprovided in accordance with the embodiment of the present invention.

First, a process at the PCR control section 22 is performed (step S10).In this process, after a PCR updating process is carried out for thoseAV devices on the 1394 bus which are 1394 devices (step S12), the CFR 44and CIR 46 are updated (step S14). During this process, informationabout the 1394 devices connected to the 1394 bus such as theirconnection statuses is collected, and the information collectedpreviously is updated.

Next, all the information contained in the CFR 44 and the CUR 46 of thepresent connection control apparatus as well as all the informationcontained in the CFRs 44 and the CIRs 46 of other connection controlapparatuses on the 1394 bus are read by the AV-device control rightjudging section 26, and based on this information a table of informationabout the rights of controlling AV devices is created (step S20). Duringthis process, the AV-device control right information table is createdfirst (step S22). To be brief, this AV-device control right informationtable is a list of the CFR information and the CIR information of allthe connection control apparatuses connected to the 1394 bus. Next, ajudgment about the AV-device control rights is made based on theAV-device control right information table as created in step S22 (stepS24). During this process, the connection statuses of the devicesconnected to the 1394 bus are analyzed and a judgment about the controlrights is made.

Lastly, a process for controlling an AV device is performed at theAV-device control section 24 by means of AV/C commands with respect toeach AV device whose control is allowed in the AV-device control rightjudging process at the step S24 (steps S30 and S32).

Each process shown in FIG. 4 will now be described in more detail.

FIG. 5 is a detailed flowchart of the process of updating the CFR 44 andthe CIR 46 shown in FIG. 4 (step 14). This process is performed at thetime when one PCR updating process performed with respect to a certainAV device by the connection control apparatus has been completed.

When this process is started, it is determined whether the PCR updatingprocess performed with respect to the certain AV device by theconnection control apparatus was a process for establishing a connectionor a process for adding or overlaying a connection (step SA10). The“establishing a connection” means that a connection is newly establishedbetween devices which have had no connection therebetween. The“overlaying a connection” means that, when a connection has already beenestablished between certain devices, a further connection is addedtherebetween or another connection is established between these devicesand another device.

Reference is now made to FIG. 9 to render the description easy tounderstand.

It is considered an establishment of connection if a connection isestablished, for example, between the AV device 80 a and the AV device80 e when no connection has been established among the AV devices 80 ato 80 e shown in FIG. 9. It is considered an overlay of connection if afurther connection is established between the AV device 80 e and the AVdevice 80 d when a connection has already been established between thesedevices, or if a connection is established between the AV device 80 eand the AV device 80 b when a connection has already been establishedbetween the AV device 80 e and the AV device 80 d.

If the result of the determination at the step SA10 is “YES”, i.e., if anew connection (which includes an overlay of a connection in this case)is established, the processing proceeds to step SA12.

In the step SA12, a process for increasing each value of the data-lengthfield F2 and the history information field F3 of the CFR 44 by one,i.e., an incrementing process, is performed. The value of thedata-length field F2 is incremented to record the fact that a newconnection has been added, while the value of the history informationfield F3 is incremented to record the fact that the CIR 46 has beenupdated. That is to say, the greater the value of the historyinformation field of the device connected to the 1394 bus, the newer therecorded information.

After the process at the step SA12 is completed, the processing proceedsto step SA14 wherein a process for adding the information about the PCRupdating process, which has actually been done, to the CIR informationis carried out. In this process, however, a value of the Info. field isset to “00”. In other words, the CIR is configured to indicate that itcontains the information of the PCR set by the present connectioncontrol apparatus. The information to be stored in the CIR 46 is shownin FIG. 3. When the process at the step SA14 is completed, the processof updating CFR and CIR is terminated.

In the case where the result of determination at the step SA10 is “NO”,then the processing proceeds to step SA16. In this step SA16, it isdetermined whether the PCR updating process was a process for releasinga connection (or a process for breaking). The term “breaking” means anoperation to release a connection which has been established betweencertain devices. When the above determination result is “YES”, theprocessing proceeds to step SA18. In the step SA18, it is determinedwhether the breaking was for the connection established by the presentnode (or the present connection control apparatus). If thisdetermination result is “YES”, the processing proceeds to step SA20 atwhich a process for decreasing by one (or decrementing) the value of thedata-length field F2 of the CFR 44 and for incrementing the value of thehistory information field F3 of the CFR 44 is performed. In other words,since the number of connections which the present connection controlapparatus controls decreases by one, the value of the data-length fieldF2 is decremented, whereas the value of the history information field F3is incremented since the CIR 46 is updated.

After the process at the step SA20 is completed, the processing proceedsto step SA22, wherein a process is performed to delete the informationof the CIRs 46 corresponding to the PCR for which the breaking was madewhich has the maximum value in the p-p counter. In this case, the CIRs46 corresponding to the PCR for which the breaking was made are thoseCIRs whose fields F5 (p), F6 (PCR[i]), F10 (objective bus ID) and F11(objective physical ID) contain the same values, respectively. When thisprocess is completed, the process for updating CFR and CIR isterminated.

In the case where the determination result at the step SA16 is “NO”, theprocessing proceeds to step SA24 at which a process for dealing with aread error is carried out since this does not correspond to a processfor establishing, overlaying, or breaking a connection.

When the determination result at the step SA18 is “NO”, the processingproceeds to step SA26. This corresponds to the case where a connectionestablished by another node (or another connection control apparatus)was released by the present node (the present connection controlapparatus itself). In the step SA26, a process for incrementing thevalues of the data-length field and the history information field of theCFR 44 is performed. After the process at the step SA26 is completed, aprocess for adding the information about the PCR updating process whichhas actually been done to the CIR information is carried out at stepSA28. In this process, however, a value “01” is set to the Info. field.The information to be stored in the CIR 46 is shown in FIG. 3. When theprocess at the step SA28 is completed, this process for updating CFR 44and CIR 46 is terminated.

A process for creating the AV-device control right information tableshown in FIG. 4 (step S22) will now be described in more detail.

FIG. 7 is a detailed flow chart of the process for creating theAV-device control right information table shown in FIG. 4 (step S22),and FIG. 6 shows one example of such tables created by the process ofthe step S22.

As shown in FIG. 6, the table contains CFR information T1, whichincludes information about the 0th to nth connection control apparatuses(n being a natural number) in the sequential order, and CIR informationT10 to T1n each suspended from a respective information portion of theCFR information Ti. That is to say, the CIR information T10′, the CIRinformation T11 . . . the CIR information T1n belong to the controlapparatuses 0, 1 . . . n, respectively.

The process for creating the AV-device control right information tablewill now be described in more detail with reference to FIG. 7. Thisprocess is performed after the updating of CFR 44 and CIR 46 shown inFIG. 5 is completed.

Upon stating this process, a process for reading the CFR 44 contained ina certain connection control apparatus on the bus is carried out (stepSB10). If the CFR 44 which has previously been read exists, then aprocess for comparing the values in the history information fields ofthe CFRs 44 for the same connection control apparatus is performed (stepSB12).

When the process of the step SB12 is completed, the processing proceedsto step SB14 at which a process is performed to determine whether thehistory information values differ or not. In other words, adetermination is made as to whether the read information of the CFR 44has been updated. If the result of this determination is “YES”, theprocessing then proceeds to step SB16. In this step SB16, a process forsetting the value of the data-length field of the CFR 44 is performed.After the process at the step SB16, a process for reading the CIR 46over the length defined by the value in the data-length field F2 set inthe process at the step SB16 is performed (step SB18).

Upon completing the process at the step SB 18, a process for storing theCFR 44 and the CIR46 as obtained in the processes at the steps SB10 andSB18 in the AV-device control right information table is performed (stepSB20). Thereafter, a process for determining whether the reading of CFRs44 has been completed with respect to all the connection controlapparatuses on the bus is performed at step SB22. If the result of thisdetermination is “NO”, then the processing returns to the step SB10. Onthe other hand, if the result of the determination at the step SB22 is“YES”, this process for creating the AV-device control right informationtable ends.

In the case where the determination result at the step SB14 is “NO”, theprocessing proceeds to the step SB22 to continue the above processes.

Next, description will be made of the AV-device control right judgingprocess (step S24) shown in FIG. 4. FIG. 8 is a flow chart showing theAV-device control right judging process (step S24) of FIG. 4 in moredetail. This process is executed by the AV-device control right judgingsection 26 (refer to FIG. 1) based on the AV-device control rightinformation table created in the above-described process as shown inFIG. 6.

When the processing starts, a process for extracting all the CIRs of thesame PCR from the AV-device control right information table is carriedout (step SC10). Here, the same PCR signifies those of the PCRs whose p,PCR[i], objective ID, and objective physical ID fields have the samevalues, respectively. When the process at the step SC10 has beencompleted, a process is performed to delete those of the CIRs extractedat the step SC10 which correspond in number to the CIRs whose Info.fields contain the value “01” sequentially from the CIR whose p-pcounter field F8 contains a greater value. In this case, however, if theCIRs extracted for the same PCR include such CIRs whose p-p counterfields F8 have the same value, the CIRs to be deleted due to their Info.fields containing the value “01” should be those which belong to theconnection control apparatus having the largest node ID number (stepSC12).

Upon completion of the process of the step SC12, a process for deletingthose CIRs whose Info. fields F9 have the value “01”, is performed (stepSC14). At the time when the process of the step SC14 is completed, aprocess for determining whether any CIRs still remain is performed (stepSC16). If the result of the determination at the step SC16 is “YES”, theprocessing proceeds to step SC18.

In the step SC18, a process for extracting that of the CIRs remainingafter the step SC14 which has the smallest value in the p-p counterfield F8. When the process at the step SC18 is completed, a process forextracting the bus ID and the physical ID of that connection controlapparatus in the AV-device control right information table to which theCIR extracted in the process of the step SC18 and for storing these IDsis performed (step SC20). By this process, the right for controlling theAV device is decided.

When the process of the step SC20 is completed, a process is carried outto determine whether the judgment about the right for controlling AVdevices has been performed with respect to all the CIRs in the AV-devicecontrol right information table (step SC22). If the result of thisdetermination is “NO”, then the processing returns to the step SC10,while this AV-device control right judging process ends if the result ofthe determination at the step SC22 is “YES”. In the case where theresult of the determination at the step SC16 is “NO”, the processingproceeds to the step SC22 to carry out the above-described determinationprocess.

Although the connection control apparatus according to the invention hasbeen described with reference to its one embodiment, the presentinvention should not be restricted only to that embodiment but canfreely be modified within the scope of the invention. For example,although the present invention has been described in the aboveembodiment as being applied to the IEEE 1394 standard, the presentinvention can be applied to any connection control apparatus connectedto a bus through which packetbased bidirectional serial communication ispossible, and to which a plurality of AV devices can be connected.

What is claimed is:
 1. A connection control apparatus adapted to beconnected to a bus through which packet-based bi-directional serialcommunication can be performed and to which a plurality of apparatusescan be connected, said connection control apparatus comprising: a memorythat stores at least a first connection status of a logical connectionof a controllable apparatus through said bus to at least one otherapparatus; and a control section that determines whether or not saidconnection control apparatus is authorized to control said controllableapparatus based on at least said first connection status.
 2. Aconnection control apparatus according to claim 1, further comprisingreading section that inputs at least said first connection status fromsaid bus and stores at least said first connection status in saidmemory.
 3. A connection control apparatus according to claim 1, whereinsaid first connection status includes information corresponding to adestination address of said controllable apparatus.
 4. A connectioncontrol apparatus according to claim 1, wherein said first connectionstatus includes information corresponding to priorities of connectionsof said controllable apparatus.
 5. A connection control apparatusaccording to claim 1, wherein said bus is a bus which complies with theIEEE 1394 bus standard.
 6. A connection control apparatus according toclaim 2, wherein said first connection status includes historyinformation of updates of said first connection status, wherein saidconnection control apparatus further comprises an updating section thatcompares a new connection status of said controllable apparatus read bysaid reading section with said first connection status stored in saidmemory, and if said new connection status is different than said firstconnection status, said updating section updates said first connectionbased on said new connection status to create an updated firstconnection status and stores said updated status in said memory.
 7. Aconnection control apparatus according to claim 1, wherein said firstconnection status includes information about another connection controlapparatus which has released said logical connection of saidcontrollable apparatus.
 8. A connection control apparatus according toclaim 4, wherein said control section determines whether or not saidconnection control apparatus is authorized to control said controllableapparatus based on said information indicative of priorities.
 9. Aconnection control apparatus connected to an IEEE 1394 bus forcontrolling a connection between apparatuses each having a plug controlregister, said connection control apparatus comprising: a plug controlregister controlling section for transmitting/receiving packets throughsaid 1394 bus to control the plug control registers of controllableapparatuses connected to said 1394 bus and to generate connectioninformation regarding connections of said controllable apparatuses tosaid 1394 bus; a control information register for storing saidconnection information generated by said plug control registercontrolling section; a control flag register for indicating a presenceof an update of said control information register and an amount ofinformation in said control information register; an apparatus controlsection for transmitting/receiving packets through said 1394 bus tocontrol operations of said controllable apparatuses connected to said1394 bus; and an apparatus control right judging section for collectingvalues in said control information register and said control flagregister with respect to all of said controllable apparatuses connectedto said 1394 bus to determine selected apparatuses of said controllableapparatuses are allowed to be controlled by said apparatus controlsection and to inform said apparatus control section of said selectedapparatuses.
 10. A connection control apparatus according to claim 9,wherein said control flag register comprises: a data-length field forrepresenting an amount of information in said control informationregister; and a history information field whose value represents apresence of an update of said control information register and isincremented each time said control information register is updated. 11.A connection control apparatus according to claim 9, wherein saidcontrol information register comprises: a first field for representingwhether said plug control register is for input or for output; a secondfield for representing a serial number of said plug control registerprovided in a corresponding apparatus of said controllable apparatuses;a third field for representing a value in a point-to-point connectioncounter of said plug control register; a fourth field for representing atype of said control information register; and objective bus ID andobjective physical ID fields for representing a bus ID and a physical IDof said corresponding apparatus provided with the plug control register.12. A connection control apparatus according to claim 11, wherein saidfourth field for representing the type of said control informationregister is a field for storing a value indicating that informationabout the plug control register set by said connection control apparatusis stored and a value indicating that information about the plug controlregister by which connection control apparatus released a point-to-pointconnection established by another apparatus is stored.
 13. A connectioncontrol apparatus according to claim 9, wherein said control flagregister and said control information register are arranged in a controlstatus register space as defined in the IEEE 1212 standard.
 14. A systemcomprising: a first connection control apparatus coupled to a busthrough which packet-based bidirectional serial communication can beperformed, wherein said first connection control apparatus comprises: afirst memory that stores at least a first connection status of a firstlogical connection of a first controllable apparatus to said bus, and afirst control section that determines whether or not said firstconnection control apparatus is authorized to control said firstcontrollable apparatus based on at least said first connection status,wherein said first connection control device is capable of establishingsaid first logical connection; and a second connection control apparatuscoupled to said bus, wherein said second connection control apparatus iscapable of establishing said first logical connection.
 15. The system asclaimed in claim 14, wherein said first control section determineswhether or not said first connection control apparatus is authorized tocontrol said first controllable apparatus based on whether said firstconnection control apparatus or said second connection control apparatusestablished said first logical connection.
 16. The system as claimed inclaim 15, wherein said first control section determines that said firstconnection control apparatus is authorized to control said firstcontrollable apparatus when said first connection control apparatusestablished said first logical connection.
 17. The system as claimed inclaim 15, wherein said first control section determines that said firstconnection control apparatus is not authorized to control said firstcontrollable apparatus when said second connection control apparatusestablished said first logical connection.
 18. The system as claimed inclaim 16, wherein said first control section determines that said firstconnection control apparatus is not authorized to control said firstcontrollable apparatus when said second connection control apparatusestablished said first logical connection.
 19. The system as claimed inclaim 14, wherein said second connection control apparatus comprises: asecond memory that stores at least said first connection status; and asecond control section that determines whether or not said secondconnection control apparatus is authorized to control said firstcontrollable apparatus based on at least said first connection status.20. The system as claimed in claim 19, wherein said first controlsection that determines whether or not said first connection controlapparatus is authorized to control said first controllable apparatusbased on whether said first connection control apparatus or said secondconnection control apparatus established said first logical connection,and wherein said second control section determines whether or not saidsecond connection control apparatus is authorized to control said firstcontrollable apparatus based on whether said first connection controlapparatus or said second connection control apparatus established saidfirst logical connection.
 21. A first connection control apparatus,comprising: a first memory that stores at least a first connectionstatus of a first logical connection of a first controllable apparatusto a bus, wherein packet-based bi-directional serial communication canbe performed via said bus; and a first control section that determineswhether or not said first connection control apparatus is authorized tocontrol said first controllable apparatus, wherein said first controlsection that determines whether or not said first connection controlapparatus is authorized to control said first controllable apparatusbased on whether said first connection control apparatus or a secondconnection control apparatus established said first logical connection.